Ion movement across excitable membranes occur through discrete entities, "channels", endowed with ion selective properties. The mechanism(s) of ion transport through and ion-selectivity of these "channels" are only partly understood, especially in mixed electrolytes. Studies on gramicidin A induced channel-mediated ion transport across artificial biomolecular lipid membranes offer unique opportunities to study mechanisms of ion transport through and ion selectivity of "narrow channels". These studies will also give information about the related problems of polypeptides (gramicidin A) within lipid bilayers. Both electrostatic interactions between "channels" and "ions", structural changes in the "channels" may play an important role in determining the ion selectivity of ion conducting channels. The present research proposal is concerned with ion transport , single and multiple, gramicidin channels in both single salt solutions and mixed electrolyte solutions. One objective of this proposal is to clarify the mechanisms of ion selectivity of the channels, especially whether structural changes of the channels play any significant role in ion selectivity. The other ojective is to obtain functional information about the molecular interactions of polypeptides, gramicidi A and some natural and synthetic analogues, within lipid bilayers. BIBLIOGRAPHIC REFERENCES: Andersen, O.S. Ion-specificity of gramicidin channels. Abstract p. 369, 5th Internation Biophysics Congress, 1975. Andersen O., S. Feldberg, H. Nakadomari, S. Levy and S. McLaughlin. A new type of electrostatic boundary potential in lipid bilayers. Biophysical Journal, p. 194a, 1976.